1. Technical Field
The present invention relates to an liquid ejecting head such as an ink jet recording head and a liquid ejecting apparatus and, more specifically, to a liquid ejecting head including a flow channel unit which defines lines of liquid flow channels extending from a common liquid chamber through pressure chambers to nozzle openings and being capable of discharging liquid from the nozzle openings as liquid drops by driving a pressure generator and a liquid ejecting apparatus having the same.
2. Related Art
Examples of a liquid ejecting head that generates pressure variations in liquid in a pressure chambers to cause the liquid to be discharged from nozzle openings as liquid drops include inkjet recording heads used for image recording apparatuses such as printers, color material ejecting heads used for manufacturing color filters for liquid crystal displays or the like, electrode material ejecting head used for forming electrodes such as Organic EL (Electro Luminescence) display and FEDs (Field Emission Displays), and biomedical organic substance ejecting heads used for manufacturing biochips.
The recording head, which is a sort of liquid ejecting head, includes lines of liquid flow channels extending from a common ink chamber (common liquid chamber/reservoir) through pressure chambers to the nozzles, generates pressure variations in liquid in the pressure chambers by activating a pressure generator such as a piezoelectric vibrator, and causes ink in the pressure chambers to be discharged from the nozzles as ink drops using the pressure variations. Some of the recording heads of the type described above include an actuator unit (vibrator unit) formed by joining a group of piezoelectric vibrators on a fixed plate and a flow channel unit formed with the ink channels fixed to a head case.
The flow channel unit includes, for example, a nozzle plate of a metal plate type formed with a plurality of nozzle openings in line, a flow-channel-formed substrate formed with flow channel bodies which serve as ink flow channels such as pressure chambers and a sealing plate (vibrating plate) that seals the openings of the flow channel bodies on the flow-channel-formed substrate, and is manufactured by integrally laminating these members. The sealing plate is formed of composite plate material, which is manufactured by laminating a resin elastic film on a metallic supporting panel such as stainless steel and removing part of the supporting plate, and is adapted to be joined to the flow-channel-formed substrate on the side of the surface with the elastic film. A diaphragm which changes the capacities of the pressure chambers is provided on the sealing plate at a portion corresponding to the pressure chambers. The diaphragm is manufactured by removing the supporting panel around and except for island portions where the distal end surfaces of the piezoelectric vibrators are joined to by etching or the like and keeping only the elastic film remained. A portion of the sealing panel corresponding to the common ink chamber is formed with ink introducing holes (liquid introducing holes) for introducing ink from a case flow channel in the head case into the common ink chamber as a part of the ink flow channels so as to penetrate through the supporting plate and the elastic film.
The head case is a member formed into a hollow block shape with, for example, synthetic resin. The head case is formed with a storage chamber which is able to accommodate an actuator unit. The storage chamber is formed so as to extend from the bottom surface of the head case, which corresponds to a surface to which the flow channel unit is joined, continuously to the upper surface opposite from the bottom surface. In other words, the storage chamber is formed as a through opening which penetrates through the head case in the direction of the height. Provided in the interior of the head case is the case flow channel penetrated through the direction of the height thereof. The upper end of the case flow channel communicates with the ink introduction channel of an introduction needle unit provided with an ink introduction needle, and the lower end of the case flow channel communicates with the ink flow channel in the flow channel unit through the ink introduction hole on the sealing plate. Therefore, the ink introduced from the ink introduction needle is supplied to the ink flow channel through the case flow channel and the ink introduction hole.
The flow channel unit is joined to the bottom surface of the head case configured as described above. More specifically, the diaphragm of the sealing plate is arranged in the opening of the storage chamber on the side of the bottom surface and the sealing plate is joined to the bottom surface of the head case by bonding or the like in a state in which the case flow channel and the ink flow channels are communicated with each other in a liquid-tight manner via the ink introducing hole, so that the flow channel unit is fixed to the head case. The actuator unit is inserted from the opening of the storage chamber on the side of the upper surface in a posture in which free ends of the piezoelectric vibrators are positioned on the distal side, and is stored in the storage chamber in a state in which the distal ends of the free ends abut against the surfaces of the island portions. Then, the distal ends of the free ends of the piezoelectric vibrators are joined to the island portions, and the fixed plate (fixed substrate) is bonded to the inner wall surface of the storage chamber so that the actuator unit is fixed in the storage chamber. JP-A-2000-006397 is an example of related art.
In the configuration described above, since the island portions of the diaphragm are electrically independent from the rest of the supporting plate, normally, there is no possibility that an electrical current flows from the island portions to the rest even when drive signals are applied to the piezoelectric vibrators. However, since the diaphragm is exposed into the storage chamber through the opening on the bottom surface of the head case, there is a case in which foreign substances such as machining chips enter into the storage chamber during the recording head assembly process, and drop onto the diaphragm. When the substances are metal or the like having electric conductivity, short-circuit between the diaphragm (that is, the island portions) and the rest of the supporting plate may occur. When such short circuit occurs, the entire supporting plate has the same potential as individual electrodes formed on the distal end surface of the piezoelectric vibrator (positive potential). On the other hand, the nozzle plate arranged on the opposite side of the supporting plate with the intermediary of the flow-channel-formed substrate is adjusted to a ground potential for preventing electrostatic charge. Accordingly, the inner peripheral surface of an ink introducing hole which is a portion of the supporting plate coming into contact with ink and the periphery of the nozzle opening of the nozzle plate serve as if they are electrodes, and hence the ink therebetween may be electrolyzed. When such electrolysis proceeds, the components in ink such as pigment is precipitated around the ink introducing hole and sludge may clog the flow channels or the nozzle openings and cause defective discharge.